This invention relates to an improved antenna structure, and method of transmission and/or reception through such an antenna, and more particularly to a dual polarized antenna for such use as citizens band (CB) radio communication.
The need for a dual polarized CB antenna has been widely recognized. See for example U.S. Pat. Nos. 2,982,959 and 3,821,742. This need arises from the fact that although virtually all mobile CB antennas are vertically polarized, as are the base stations, experience has shown that much signal reception is by way of reflections from buildings and reradiations from power lines and the like. As a result, communications between vertical antennas has been erratic. The polarization of signals can be rotated by multiples of about 90.degree. at any given location resulting in a "dead spot" at that location, and reduced signal at other locations where the rotation is less than 90.degree.. It would be desireable to transmit radiation polarized at an angle between the vertical and the horizontal, for example 45.degree..
It has been found that such a 45.degree. polarization is achieved when both vertical and horizontal radiators are fed equal energy in an antenna couplet comprised of a quarter wave vertical radiator with its lower end positioned in the center of a horizontal dipole radiator. There is then achieved a bi-directional gain of 1.5 db in the horizontal pattern and some gain in the vertical pattern as well, depending upon the height of the antenna couplet above ground. This makes an antenna couplet very useful in radio communications where it is desirable for radiation to take place simultaneously in both the vertical and horizontal polarization modes, especially if the same type of antenna couplet is used to receive the radiation at the opposite end of the communication path in which case the gains just mentioned are doubled.